This invention relates generally to inkjet printhead fabrication processes and more particularly to methods for fabricating fully integrated inkjet printheads on a substrate.
There are known and available commercial printing devices such as computer printers, graphics plotters and facsimile machines which employ inkjet technology, such as inkjet pens. An inkjet pen typically includes an ink reservoir and an array of inkjet printing elements. The array is formed by an inkjet printhead. Each printing element includes a nozzle chamber, a firing resistor and a nozzle opening. Ink is stored in the reservoir and passively loaded into respective firing chambers of the printhead via an ink refill channel and respective ink feed channels. Capillary action moves the ink from the reservoir through the refill channel and ink feed channels into the respective firing chambers. Printer control circuitry outputs respective signals to the printing elements to activate corresponding firing resistors. In response an activated firing resistor heats ink within the surrounding nozzle chamber causing an expanding vapor bubble to form. The bubble forces ink from the nozzle chamber out the nozzle opening. An orifice plate adjacent to the barrier layer defines the nozzle openings. The geometry of the nozzle chamber, ink feed channel and nozzle opening defines how quickly a corresponding nozzle chamber is refilled after firing.
To achieve high quality printing ink drops or dots are accurately placed at desired locations at designed resolutions. Printing at resolutions of 300 dots per inch and 600 dots per inch is known. Higher resolutions also are being sought.
A monolithic structure for an inkjet printhead is described in copending U.S. patent application Ser. No. 08/597,746 filed Feb. 7, 1996 for xe2x80x9cSolid State Ink Jet Print Head and Method of Manufacture.xe2x80x9d The process described therein includes photoimaging techniques similar to those used in semiconductor device manufacturing. The printing elements of a monolithic printhead are formed by applying layers to a silicon die. The firing resistors, wiring lines and nozzle chambers are formed by applying various passivation, insulation, resistive and conductive layers on the silicon die. Such layers are referred to collectively as a thin film structure. An orifice plate overlays the thin film structure opposite the die. Nozzle openings are formed in the orifice plate in alignment with the nozzle chambers and firing resistors. The geometry of the orifice openings affect the size, trajectory and speed of ink drop ejection. Orifice plates often are formed of nickel and fabricated by lithographic and electroforming processes.
According to the invention, a monolithic inkjet printhead is formed using fabrication processes working from one face of the die. According to one aspect of the invention, the printing elements are formed by processes working from such one face of the die. According to another aspect of the invention, feed channels are formed by processes working from the same one face of the die. This single-sided fabrication process is distinguished from fabrication processes that form printing elements by processes working from one face of the die and that form the feed channels by processes working from an opposite face of the die. The die includes a top surface, a bottom surface and four edge surfaces extending between the top surface and bottom surface. According to the invention, the fabrication processes do not act from both the top surface and bottom surface. For a naming convention in which the printing elements are formed at the top surface, the fabrication processes work from the top surface and not the bottom surface. In some embodiments an etching step works from both the top surface and an edge surface to remove filler material.
According to another aspect of the invention, a monolithic inkjet printhead includes a plurality of feed channels. Each feed channel is formed as a recessed area relative to a first surface of a die. A thin film structure is applied to such first side of the die over the feed channels. The monolithic inkjet printhead includes a plurality of printing elements. The printhead is formed in part by a die having a first surface, an opposite second surface, and an edge surface extending from the first surface to the second surface. The recessed area extends along the first surface from an edge surface inward away from the edge surface. The feed channel does not extend to the second surface. The printhead also is formed in part by a plurality of first layers overlaying the first surface of the die, and a second layer overlaying the plurality of first layers. The plurality of first layers are patterned to define a plurality of firing resistors, wiring lines and ink feed channels. The plurality of first layers define the thin film structure. The second layer has a pattern defining a plurality of nozzle chambers. Each one of the plurality of nozzle chambers is aligned over at least one firing resistor of the plurality of firing resistors. Each one of the plurality of nozzle chambers has a nozzle opening. Each one of the plurality of printing elements includes a firing resistor and nozzle chamber, a fill channel and a feed channel. The fill channel extends from the nozzle chamber to the feed channel. For each one of the plurality of printing elements a respective wiring line is conductively coupled to the firing resistor of said one printing element.
These and other aspects and advantages of the invention will be better understood by reference to the following detailed description taken in conjunction with the accompanying drawings.